The islanding detection for photovoltaic grid-connected generation systems

In photovoltaic grid-connected generation systems, whether the condition of islanding can be detected effectively and timely or not is of great significant for the entire grid-connected system. The features and disadvantages of the conventional active frequency drift (AFD) method are analyzed for islanding detection. And on this basis, a novel active frequency drift method with comparison of positive and negative frequency (AFDCPNF) is proposed. For different nature of the load, the improved method can rapidly detect the islanding, reduce the non-detection zone (NDZ) and improve the reliability of a grid-connected system. The experimental results verify the effectiveness of the advanced detection method.